COMBINED SCIENCE 0653/62

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Cambridge IGCSE™

COMBINED SCIENCE 0653/62

Paper 6 Alternative to Practical February/March 2021

1 hour

You must answer on the question paper.

No additional materials are needed.

INSTRUCTIONS ● Answer all questions. ● Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs. ● Write your name, centre number and candidate number in the boxes at the top of the page. ● Write your answer to each question in the space provided. ● Do not use an erasable pen or correction fluid. ● Do not write on any bar codes. ● You may use a calculator. ● You should show all your working and use appropriate units.

INFORMATION ● The total mark for this paper is 40. ● The number of marks for each question or part question is shown in brackets [ ].

*9751707663*

DC (CJ/JG) 208154/2© UCLES 2021 [Turn over

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1 A student investigates the rate of respiration in yeast cells. Yeast is a single-celled organism similar to plant and animal cells.

The student is provided with a yeast suspension and some yeast suspension that has been boiled.

As yeast cells respire they produce carbon dioxide gas.

(a) Describe the observation that shows that a gas is made in a liquid.

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(b) The student does the following procedure:

Step 1 puts 1 cm3 distilled water into a test-tube labelled A

Step 2 fills test-tube A to the top with yeast suspension

Step 3 puts 1 cm3 5% glucose solution into a test-tube labelled B

Step 4 fills test-tube B to the top with yeast suspension

Step 5 puts 1 cm3 5% glucose solution into a test-tube labelled C

Step 6 fills test-tube C to the top with boiled yeast suspension

Fig. 1.1 shows the filled test-tubes.

waterand yeast

suspension

glucose solutionand yeast

suspension

test-tube A test-tube B test-tube C

glucose solutionand boiled yeast

suspension

Fig. 1.1

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Step 7 places a large test-tube (boiling tube) over the top of each of the test-tubes A, B and C

Step 8 turns the test-tubes upside down as shown in Fig. 1.2

filled test-tube large test-tubeplaced over thetop of filledtest-tube

both test-tubesquickly turnedupside down

Fig. 1.2

Step 9 places all of the test-tubes into a water-bath at 40 °C

Step 10 leaves the test-tubes in the water-bath for 5 minutes.

If gas is made in the small test-tube, the liquid is pushed out into the large test-tube.

After 5 minutes the student measures the height of the liquid in each large test-tube (boiling tube), as shown in Fig. 1.3.

height of liquid inlarge test-tube

gas made

Fig. 1.3

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The results are recorded in Table 1.1.

Table 1.1

test-tube height of liquid/ mm

A 18

B

C 5

(i) Fig. 1.4 shows the height of liquid in the large test-tube around test-tube B.

Fig. 1.4

Measure this height to the nearest mm and record it in Table 1.1. [1]

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(ii) Test-tube B contains glucose.

Test-tube A contains no glucose.

Use this information to explain the difference in the results for test-tube B and test-tube A.

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(iii) Test-tube C is used as a type of control.

Explain the purpose of this control.

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(iv) Explain why it is difficult to get an accurate value for the height of a liquid in a test-tube.

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(v) Describe a test to find out if the gas made is carbon dioxide. Include the observation for a positive result.

test ....................................................................................................................................

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observation ........................................................................................................................ [1]

(vi) State one variable that is kept constant in this investigation.

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(c) The teacher does a similar experiment at 40 °C to investigate the effect of different concentrations of glucose on the yeast suspension. The teacher measures the volume of gas collected after 5 minutes.

The results are shown in Table 1.2.

Table 1.2

percentage concentration of glucose solution

volume of gas collected after 5 minutes

/ cm3

6 3

7 8

8 7

9 18

10 23

11 23

(i) The result for 8% glucose solution is anomalous.

Suggest what might have caused this anomalous result.

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..................................................................................................................................... [1]

(ii) Predict the expected volume of gas for the 8% glucose solution.

....................................................cm3 [1]

(iii) Describe the relationship between the percentage concentration of glucose solution and the volume of gas made.

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..................................................................................................................................... [2]

(iv) Suggest a piece of apparatus suitable for collecting the gas and measuring its volume.

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(v) The teacher repeats their investigation at 20 °C instead of 40 °C. Suggest what effect, if any, a lower temperature has on the results.

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[Total: 13]

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2 A student prepares a sample of the insoluble salt barium sulfate by reacting aqueous copper(II) sulfate with aqueous barium nitrate.

(a) Procedure

The student:

• measures 15 cm3 of aqueous copper(II) sulfate and pours it into a beaker

• measures 7.5 cm3 of aqueous barium nitrate and pours it into the beaker

• stirs the reaction mixture

• filters the reaction mixture and collects the blue filtrate in a conical flask.

(i) Explain why a 10 cm3 measuring cylinder is used to measure the aqueous barium nitrate rather than a 25 cm3 measuring cylinder.

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..................................................................................................................................... [1]

(ii) State one observation of the filtrate in the conical flask that shows it contains copper(II) ions.

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(b) The residue of barium sulfate on the filter paper is impure.

(i) The impure residue contains some soluble copper(II) compounds.

Describe how the student purifies the barium sulfate by removing the soluble copper(II) compounds from the residue.

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..................................................................................................................................... [1]

(ii) State the colour of the purified barium sulfate precipitate.

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(c) The student tests two samples of the filtrate.

Here is a page from the student’s notebook.

With four drops of sodium hydroxide solution = blue precipitateWith a little aqueous ammonia the filtrate gives a blue precipitate

There is a blue precipitate when lots of sodium hydroxide solution is addedGives a dark blue solution when lots of aqueous ammonia is added

Present these results in a results table.

Include the headings for the table, the tests used and the observations.

[3]

[Total: 7]

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3 Calcium hydroxide is a white solid that is added to acidic soils to increase their pH.

Calcium hydroxide neutralises acids such as dilute nitric acid to make a salt and water. Plan an investigation to find out how the pH of dilute nitric acid changes as calcium hydroxide is

added to the acid.

You are provided with:• calcium hydroxide powder • dilute nitric acid• Universal Indicator solution.

You may use any common laboratory apparatus in your plan.

In your plan, include:

• the apparatus needed• a brief description of the method and explain any safety precautions you should take• what you would measure• which variables you would keep constant • how you would process your results to draw a conclusion.

You may include a labelled diagram if you wish.

You may include a table that can be used to record the results if you wish.

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4 A student investigates the rate at which hot water cools.

(a) Procedure The student:

• ¾ fills a beaker with water at room temperature

• records in Table 4.1 the initial temperature of the water in the beaker

• half-fills a test-tube with hot water

• records in Table 4.1 the initial temperature of the hot water in the test-tube

• secures the test-tube in the beaker so that the hot water level is below the level of the water in the beaker

• records in Table 4.1 the temperature of the water in the beaker and the temperature of the water in the test-tube every 30 s for 180 s.

(i) Fig. 4.1 shows an incomplete diagram of the student’s experiment.

Complete Fig. 4.1 by: • marking the hot water level in the test-tube

• adding a thermometer to measure the temperature of the hot water.

beaker test-tube

thermometer

water atroomtemperature

Fig. 4.1 [2]

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(ii) Fig. 4.2 shows the thermometer readings at 180 s. Record these temperatures in Table 4.1.

20

30

°C

20

30

°C

water inbeaker

water intest-tube

Fig. 4.2

Table 4.1

time/ s

temperature of water in

beaker / °C

test-tube / °C

0 23.5 76.0

30 23.5 57.0

60 23.5 45.0

90 23.5 38.0

120 24.0 33.5

150 24.0 30.0

180 [3]

(iii) Describe one practical technique the student uses to ensure that the temperature of the water in the beaker is measured accurately.

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(iv) Suggest why the temperature of the water in the beaker changes during the experiment.

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(b) (i) Plot a graph of the temperature of the hot water in the test-tube (vertical axis) against time using the results in Table 4.1. Do not start the temperature scale at 0 °C.

[3]

(ii) Draw the best-fit curve. [1]

(c) (i) Calculate the rate of cooling of the hot water in the test-tube during the first 30 s. Use the equation shown.

rate of cooling during first 30 s = temperature at 0 s – temperature at 30 s

30

Give your answer to two significant figures.

rate of cooling = ................................................. °C / s [1]

(ii) Describe how the rate of cooling of the hot water in the test-tube changes during the 180 s.

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[Total: 13]

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Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity.

To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cambridgeinternational.org after the live examination series.

Cambridge Assessment International Education is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of the University of Cambridge Local Examinations Syndicate (UCLES), which itself is a department of the University of Cambridge.

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COMBINED SCIENCE 0653/62